GEOTRACES: Inspired by GEOSECS to investigate trace elements and their isotopes in the ocean

Goldschmidt 2019 – Session 08m

Robert F. Anderson, Lamont-Doherty Earth Obs. Roger Francois, Univ. British Columbia Martin Frank, GEOMAR, Helmholtz Centre Ocean Res. Gideon Henderson, Univ. Oxford, Earth Sciences Catherine Jeandel, LEGOS, Toulouse Mukul Sharma, Dartmouth Coll., Earth Sciences

http://www.geotraces.org/ GEOTRACES: An international study of the marine biogeochemical cycles of trace elements and their isotopes

August 2019: • Cruises completed: 113 • Nations supporting cruises: 17 • Publications: > 1200 • Data shared publicly: http://www.geotraces.org/dp/idp2017

GEOTRACES: An international study of the marine biogeochemical cycles of trace elements and their isotopes

Inspired by GEOSECS . . .

. . . what do they have in common?

GEOTRACES: An international study of the marine biogeochemical cycles of trace elements and their isotopes

Inspired by GEOSECS . . .

. . . what do they have in common?

Both were created to address problems to large to be achieved without a large coordinated effort.

Large programs are required to address certain complex topics in oceanography

Selected historical examples

• Overturning circulation of the ocean

• Ocean-atmosphere partitioning of (both natural and anthropogenic)

• Global biogeochemical cycles

Birth of GEOSECS – To quantify the rate of ocean overturning circulation

Henry Stommel

Motivated GEOSECS by identifying a problem too large to solve without a large program

Photo from chapter by Walter Munk in 50 years of Ocean Discovery Atlantic early 14C data helped constrain rate of overturning circulation (Broecker et al., JGR 1960)

North South

West

East Birth of GEOSECS

“Ed Goldberg (Scripps Institution of Oceanography) and I were attending some sort of meeting at WHOI during the late 1960s. Hank came to us and said that radiocarbon measurements in the sea were of great importance. He went on to gently chastise us (the geochem community) for doing only scattered stations.

What is needed, he said, is a line of stations extending the length of the Atlantic.

Gee, we said, that would cost a million dollars, a sum greater than the entire NSF annual budget for .

Hank replied, “Well it would be worth more than a million.”

Quote from Wally Broecker repeated in John Farrington’s chapter in 50 Years of Ocean Discovery - Confirmed by personal communication with Wally Harmon Craig Karl Turekian

Wally Broecker

Arnold Joe Reed Bainbridge

GEOSECS 1972-1978 First global survey of ocean chemistry 28 Investigators, 14 institutions, $24M Slide Courtesy Chris Measures Derek Spencer John Edmond GEOSECS Success – Ocean Ventilation Time Scales

Derek Spencer Broecker & Wally Broecker Peng 1982 Arnold Bainbridge GEOSECS Success: First assessment of the

ocean’s uptake of anthropogenic CO2 GEOSECS Success – Foundation for Future Programs

• TTO - Transient Tracers in the Ocean

• WOCE - World Ocean Circulation Experiment

• JGOFS - Joint Global Ocean Flux Study (JGOFS)

• CLIVAR Repeat Hydrography (GO-SHIP)

• GEOTRACES

• and more

Where’s Wally? Trace elements and their isotopes

GEOSECS + 20 to 30 years

History repeats itself (there is a lesson here) Two decades of work on iron was insufficient to characterize its biogeochemical cycle

Stations as of 2003 with dissolved Fe data to depths > 2000 m - Compiled by Payal Parek Reproduced from Anderson et al., 2014 Two decades of work on iron was insufficient to characterize its biogeochemical cycle

Situation ca. 2000 was even worse for other trace elements and isotopes. A new strategy was needed. GEOTRACES: Timeline – Selected milestones Lesson: Be patient

2000 Initial discussions and planning for “GEOSECS-II” 2001 Special session & Town Hall to assess interest 2003 International planning workshop – define goals 2004 SCOR accepts oversight 2005 Initiate data management 2006 Complete science plan 2006 Initiate intercalibration 2007 Pilot studies – International Polar Year 2010 Launch main field program 2014 Release of first data product 2015 Launch synthesis initiative 2017 Second data product 2019 Mid-life review GEOTRACES Discoveries – Prominent Fe sources from ridges and margins

Fe residence time is so short that its distribution is dominated by its sources

Clear source signatures: - Dust - Sediment - Hydrothermal - Rivers

Source: www.eGEOTRACES.org

GEOTRACES Discoveries – Prominent Fe sources from ridges and margins

Fe residence time is so short that its distribution is dominated by its sources

Clear source signatures: - Dust - Sediment - Hydrothermal - Margins

Source: www.eGEOTRACES.org

GEOTRACES Discoveries – Dual behavior of Co

• Dominant source in shelf & upper slope sediments • Cycles with P in the upper water column (nutrient)

(A) • Scavenged by Mn in deep water • Residence time • ~ 7 yrs in upper 250 m • ~1000 yrs in deep sea • Most Co in pelagic sediments derived from (B) upper ocean

Top: Atlantic zonal Co section (Noble et al., 2017) Bottom: Pacific zonal Co section (Hawco et al., 2016, 2018)

Figure 5. Concentrations of dissolved Co measured along zonal GEOTRACES sections (A) between North America and North Africa (Noble et al 2017) and (B) between Peru and Tahiti (Hawco et al 2016). Dissolved oxygen concentrations are overlain as contours. Elevated Co concentrations are seen within low-oxygen water on the eastern boundary of each section, thought to reflect mobilization of Co bound to Mn oxides that are reduced in organic-rich upper margin sediments, and within Labrador Seawater roughly between 1000 m and 2000 m depth on the western boundary in (B). Data are available in the GEOTRACES Intermediate Data Product IDP2017 (Schlitzer et al 2018). Figure produced using Ocean Data View < http://odv.awi.de>.

Tracers in the Sea – 1982 Wally set the standard for synthesis of findings

Aboard the Knorr

In his Lamont Office

Photos from Patty Catanzaro GEOTRACES Synthesis Themes/Goals: Identify processes and quantify fluxes

- Inputs and outputs at the interfaces of the ocean - Internal cycling within the ocean Uncertainty about iron emphasizes need for better fluxes and residence times 1000

100

10

Iron Residence Time (years) Time Iron Residence 1 1 10 100 Global Iron Supply (Gmol/yr)

- Output from 13 global ocean biogeochemical models - Two orders of magnitude uncertainty (range among models) Tagliabue et al., 2016 GEOTRACES Synthesis: Quantifying fluxes and comparing different approaches

Solid-phase 230Th mass balance 25 Model Core top

/yr) 20 2 230Th-norm susp. part. flux 15 Sinking rate suspended particles

10 Dust flux (g/m Comparison of 8 methods to 5 estimate dust flux. Phil. Trans. Roy. Soc. A, 2016 0 -50 -40 -30 -20 Longitude GEOTRACES Synthesis: Combining trace elements & radionuclides to estimate residence times

Full water column replacement times (red bars): Shorter than previous estimates for Fe and Mn Hayes et al., GBC, 2018 GEOTRACES Synthesis: Current and future work

• Many studies quantifying fluxes and residence times.

• Micronutrient speciation and bioavailability

• Identifying new processes not yet in models

Following the spirit of GEOSECS synthesis led by Wally Broecker GEOSECS Original Panel Members

Wallace S. Broecker Lamont-Doherty Geological Observatory Harmon Craig Scripps Institution of Oceanography H. Göte 0stlund University of Miami P. Kilho Park Oregon State University Joseph L. Reid Scripps Institution of Oceanography Derek W. Spencer Woods Hole Oceanographic Institution Henry M. Stommel Massachusetts Institute of Technology Taro Takahashi Institute of Technology* (LDEO) Karl K. Turekian Yale University Herbert L. Volchok Atomic Energy Commission

From Turekian, 1970, JGR Intro to special issue on GEOSECS test station